In windows of motor vehicles, such as electric train, automobile and the like, it is general to mount a plate glass to a metal vehicle body by using a plastic frame.
In recent years, such plastic frame is directly molded on a plate glass by subjecting a fluid resin to an extrusion molding or injection molding, and the frame-mounted plate glass consisting of the plate grass and the frame integrally mounted thereto is used as a part of assembling the vehicle body.
As is seen from FIG. 5, in case of producing a frame-mounted plate glass by injection molding, a plate glass 5 is held between an upper die 2 and a lower die 3 in a manner to form a cavity 4 therearound for the frame. Into the cavity 4, there is injected a fluid resin (or melted resin) for the frame. After the fluid resin in the cavity 4 solidifies, the upper die 2 is removed and a frame-mounted plate glass thus produced is removed from the lower die 3 for the production of the frame-mounted plate glass.
Since, during the injection molding, the plate glass is kept pressed by the die and a high temperature and high pressure fluid melted resin is injected into a surrounding portion of the plate glass, the plate glass is applied with a complicated stress, which tends to induce breakage of the plate glass.
One of the methods for detecting such breakage of the plate glass during injection molding is shown in Patent Document 1.
In case of integrally molding the frame onto plate glass by injection molding, usage of a dummy plate is proposed by Patent Document 2 as a technique for suppressing breakage of the plate glass.
The breakage of the plate glass occurs mainly near a gate of the die, and thus Patent Document 3 proposes provision of a plurality of gates in the injection molding die.